The invention concerns a method and a device for the continuous casting and direct deformation of a metal strand, especially a cast steel strand, which has a rectangular format or the format of a bloom, preliminary section, billet, or round, is guided in a curved strand guide after the continuous casting mold, subjected to secondary cooling with a liquid coolant, and prepared in an automatically controlled way for the deformation pass at a uniform temperature field in the strand cross section.
In general, in the continuous casting of different steel grades and dimensions or formats, one's attention is directed at the strand shell growth during secondary cooling and at the position of the tip of the liquid crater in a deformation line. It is known, for example, from EP 0 804 981 that the cast strand can be sufficiently compressed in the deformation line to produce the desired final thickness. However, this makes it necessary to determine the position of the tip of the liquid crater, based upon which the deformation force is applied horizontally along a wedge-shaped surface. However, a process of this type is relatively coarse and does not take into account the state of the microstructure that is to be expected. The reason lies in the unsatisfactory heat distribution due to unfavorable cooling and uniform strand support with nonuniform heat dissipation from the strand cross section. Adjustment of the secondary cooling to the strand support does not occur, either. To improve these conditions, it was proposed in German Patent Application 100 51 959.8, which has not been pre-published, that the secondary cooling be analogously adapted in its geometric configuration to the solidification profile of the cast strand on the following traveling length of the cast strand. The strand support is likewise analogously reduced as a function of the solidification profile of the cast strand at the respective travel length. In this connection, with increasing travel length, the corner regions of the cast strand cross section are less cooled than the middle regions. In the realization of this process, the spray angles of the spray jets in the secondary cooling are adjusted to the strand shell thickness in such a way that a low spray angle is assigned to a decreasing liquid crater width. A significant equalization of the temperature in the strand cross section over layers of the strand cross section is already achieved by these measures.
With this knowledge, the inventor of the above-cited, unpre-published patent application further recognized that the manner in which the process of so-called soft reduction of the cast strand is carried out must be further optimized. This recognition is based on the fact that high deformation resistance due to unfavorable temperature distribution in the cast billet or in the cast preliminary section with variable ductility causes variable deformation resistance and variable strain and thus leads to cracking.
An improvement of the internal quality of cast strands with different cross-sectional shapes and dimensions, especially with respect to positive segregation, core porosity, and core breakdown, requires a reduction process in the solidification range. The previously used procedure, e.g., with billet cross sections, leads to circular solidification with circular isotherms in the cross section, which develop in the region of the bending and straightening driver. Since only a reduction in the core is possible with this type of temperature distribution, only a mechanically influenced final solidification is achieved. However, the results are unsatisfactory and subject to very strong fluctuations. The reason is that the region of final solidification is very difficult to determine.